1. Field
The disclosed embodiments relate to numerical-control machine tools for machining parts or workpieces with at least one large dimension. More specifically they relate to a machining device in which the workpiece is positioned in a fixed manner on a fixed table above the machining means, and in which the machining tools move during the machining operations.
2. Brief Description of Related Developments
When workpieces are of large dimensions, and therefore difficult to fix and hold in a precise position, the solution employed is to hold the workpiece immobile on a table, which is also immovable, rigid, and very firmly fixed, and to move the tools that are to machine the workpiece by means of a gantry above the table.
The gantry generally comprises a horizontal crossmember supported by two side posts.
The gantry travels along one of the axes of the table, specifically the longest axis, and bears on high precision sliding tracks fixed to the table. It carries one or more machining heads that travel along the horizontal crossmember of the gantry.
The machining head or heads are also capable of executing various movements necessary for machining movements of translation to bring the machining tool towards the table, and in certain cases movements of rotation to tilt the axis of rotation of the machining tool.
Machines of this type are very common in the industry and enable very long tables, sometimes exceeding several tens of meters, to be used.
However, machines of this type have several drawbacks which complicate their use and reduce their industrial profitability.
On the one hand, gantries, owing to the complexity of the machining heads which they support and the necessary precision of the machining operations, have to be as rigid as possible. To achieve this rigidity, gantries have to be very voluminous and very heavy, with weights of 20 or 30 tons or more, which complicates their movements and in practice limits the speeds of travel, particularly when not engaged in machining.
On the other hand, gantries operate by machining workpieces placed on the top of the table, from above, causing a buildup of chips of material removed by the machining action and necessitates the provision of means of removal which may make it necessary to interrupt the machining operations.